This invention relates in general to electrophotography and in particular to a process for preparing an electrophotographic imaging member.
In electrophotography, an electrophotographic plate containing a photoconductive insulating layer on a conductive layer is imaged by first uniformly electrostatically charging its surface. The plate is then exposed to a pattern of activating electromagnetic radiation such as light. The radiation selectively dissipates the charge in the illuminated areas of the photoconductive insulating layer while leaving behind an electrostatic latent image in the non-illuminated areas. This electrostatic latent image may then be developed to form a visible image by depositing finely divided electroscopic marking particles on the surface of the photoconductive insulating layer. The resulting visible image may then be transferred from the electrophotographic plate to a support such as a paper. This imaging process may be repeated many times with reusable photoconductive insulating layers.
During machine function, a photoconductive imaging member is constantly under repetitive electrophotographic cycling which subjects the electrically operative layers to high electrical charging/discharging cycles, multiple exposures to light for latent imaging development and erasure, and heat due to temperature elevation as a result of machine operation. The repetitive electrical and light fatigue lead to a gradual deterioration in the electrical characteristics of the imaging member, and limit its service life in the field. In the attempt to fabricate a robust photoconductive imaging system, many innovative ideas have been attempted with the intent to overcome this shortfall and extend the electrical functional life of the imaging member.
Modern composite imaging members have been developed having numerous layers, which are highly flexible and exhibit predictable electrical characteristics within narrow operating limits to provide excellent images over many thousands of cycles. One type of multilayered photoreceptor that has been employed as a belt in electrophotographic imaging systems comprises a substrate, a conductive layer, a blocking layer, an adhesive layer, a charge generating layer, and a charge transport layer. This photoreceptor may also comprise additional layers such as an anti-curl layer and an optional overcoating layer.
Various coating methods are used for applying layers in a multi-layer electrophotographic imaging member. The methods include dip coating, roll coating, Meyer bar coating, bead coating, curtain flow coating, vacuum deposition and solution coating. U.S. Pat. No. 4,082,551 to Steklenski et al. discloses a process of coating multiple layers onto an insulating, polyester substrate by applying solutions having the coating substance dissolved therein and drying each applied layer before coating a subsequent layer.
U.S. Pat. No. 4,571,371 to Yashiki discloses an electrophotographic photosensitive member having a charge generating layer and a charge transport layer. A dispersion of charge generating material dissolved in solvent is applied to a cured polyamide resin layer by soaking and drying at 100.degree. C. for 10 minutes to form a charge generating layer. Subsequently, a solution containing a charge transfer material is applied to the dried charge generating layer followed by drying at 100.degree. C. for 60 minutes to form a charge transfer layer.
U.S. Pat. No. 4,579,801 to Yashiki discloses a process for applying a dispersion of charge generating material in a solution containing a binder resin to a suitable substrate or dried underlayer. The charge generation layer can be formed by vapor deposition.
U.S. Pat. No. 4,521,457 to Russell et al. discloses a process for simultaneously constraining two different coating materials and forming on a substrate a continuous, unitary layer comprising adjacent "ribbons," each ribbon comprised of different materials and in edge-to-edge contact with an adjacent ribbon. The coated ribbons are dried in two zones, one at about 57.degree. C. and another at about 135.degree. C. The process is suitable for producing electrophotographic imaging members utilizing multi-active layers.
U.S. Pat. 4,855,203 to Badesha et al. discloses a solution process for the preparation of photogenerating compositions for use in photoconductive imaging members. A photoconductive layer is prepared by a process that comprises dissolving an inorganic photoconductive component in a solvent, removing suspended particles, depositing the resulting solution on a supporting substrate followed by heating.
The present invention relates to a process for preparing an electrophotographic imaging member. The process results in a photoreceptor that surprisingly exhibits lower dark decay and greater infra-red photosensitivity.